A photovoltaic array for converting solar energy to electrical power may include several hundred photovoltaic (PV) panels mounted on the roof of a building or a mechanical support structure located close to local electrical loads. On a much larger scale, a PV array operated by an electric power utility may include more than one hundred thousand PV panels electrically interconnected in large groups on tens of thousands of square feet (thousands of square meters) of land area. It is well known that a reduction in output power from a small number of PV panels in a PV array may substantially reduce output power from the entire array. Output power from a PV panel may be reduced by, for example, a shadow falling across part of the PV panel's photosensitive surface, high temperature in part of the PV panel, aging effects, or dust, water, or debris accumulating on the PV panel. Power output may also be reduced by mechanical damage to the relatively brittle silicon material commonly used in the manufacture of commercially available PV panels. Corrosion in electrical connectors and conductors used to interconnect PV panels is also known to reduce PV array output power.
Power output from a PV array may be monitored to determine if PV panels within the array have malfunctioned or are otherwise operating with reduced power output. When an unexpected reduction in PV array output power is detected, it is desirable to determine which PV panel or panels are causing the power reduction. However, since the outputs of many PV panels are combined together in a PV array, it may be difficult to determine which panel or panels are related to an observed reduction in PV array output power.
The time and effort needed to locate a damaged or poorly performing PV panel increases as the number of PV panels in a PV array increases. Troubleshooting a PV array also becomes more difficult and expensive when access to individual PV panels is limited, for example PV panels mounted on top of tall structures or PV panels spaced close together in a large PV array. Furthermore, there are safety hazards associated with placing personnel in proximity to an operating PV array, for example hazards from high voltage, high current, intense direct and reflected sunlight, injuries from falls or from lifting heaving objects, and so on. Because of these hazards, a PV array may be shut down to permit inspections to be conducted in a safe manner. Or, a PV array may be operated with reduced power output until inspections and repairs can be conducted at night. Consequences of shutting down a PV array or operating a PV array at reduced power include, for example, loss of revenue from the sale of electricity, inadequate power available to operate electrical loads, and insufficient voltage output from the array for supplying power to an electrical grid.
What is needed is a simple, reliable, cost-effective system for monitoring the operating status of PV panels in a PV array and for sending information on PV panel status to a central monitoring and control system. What is further needed is a system for identifying and locating a particular PV panel having values of selected operating parameters outside a range for each parameter, so that damaged or degraded PV panels may be quickly located and repaired or replaced.